Make all of the rest of the code base be conditionally compiled.

NXDNSACCH.cpp

@@ -1,5 +1,5 @@
 /*
-*   Copyright (C) 2018 by Jonathan Naylor G4KLX
+*   Copyright (C) 2018,2023 by Jonathan Naylor G4KLX
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
@@ -17,11 +17,12 @@
 */
 
 #include "NXDNSACCH.h"
-
 #include "NXDNConvolution.h"
 #include "NXDNDefines.h"
 #include "NXDNCRC.h"
 
+#if defined(USE_NXDN)
+
 #include <cstdio>
 #include <cassert>
 #include <cstring>
@@ -212,3 +213,6 @@ CNXDNSACCH& CNXDNSACCH::operator=(const CNXDNSACCH& sacch)
 
 	return *this;
 }
+
+#endif
+